I haven't tried this but, according to my info the "defroster flap closed" element is more or less to the right of the cluster towards the top of the box. My info as tells you to remove the dash pad. I'd pull the cluster and look right, if you see it, manually close it and see if the air stops from the defroster. Then you know you have it. Keep in mind that this flap is naturally open and other vacum leaks will cause it to open, check the system correctly first.
The switchover valves are behind the glove box according to my info for a 89 107 chassis.
#2 center flap
#1 legroom flap
#3 defroster flap
#4 recirc flap elements (the most common failure)
vacum supply in is to the side of it, according to my pic, it comes in beside #2, the outputs are seperated from each other unlike the supplys.
Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.